This invention generally relates to a manufacturing process for making lightweight, fabric-reinforced, elastomeric fuel tanks and more particularly to the manufacture of complex-shaped tanks of the type which are installed within the body framework or complex shaped cavity of an aircraft and/or road vehicle.
Fuel tanks of the type alluded to, and especially those which are made for aircraft installations, have been made for many years by a labor-intensive, inside-to-outside layup process. According to one of these prior art processes, a plaster/wood-wool mixture is formulated and applied to a mold fixture having the approximate configuration of the body framework cavity into which the fuel tank is to be installed. The fixture however is made undersized by an amount equal to the wall thickness of the finished tank. The plaster is cured for approximately 48 hours and removed from the fixture and the resultant male plaster form is used for layup of the fuel tank structure. Accordingly, and because it is a male form, the first ply of material applied to the plaster form will constitute the interior facing of the finished tank. Therefore, and to eliminate any possible discontinuities in the composite structure which may compromise the leak-proof integrity of the tank, the plaster form must be made as smooth as possible. Consequently, the plaster is hand-sanded to a smooth finish and then the various fittings which are required for the finished tank are mounted thereon. Finally, the materials forming the composite of the tank wall structure are applied to the plaster form and cured into an integral structure. Upon completion of the cure, the plaster form must be removed from the inside of the tank. This is accomplished by soaking the plaster in hot water, breaking it up into small pieces, and washing it out of the tank through one or more of the access fittings provided in the tank wall. Obviously, it is extremely important that all of the plastic is removed from the interior of the tank or contamination of the fuel will result.
Exemplary of the prior art pertaining to fuel tank manufacturing and the use of male forms are U.S. patents to E. M. Scharenberg (U.S. Pat. No. 2,394,492); M. R. Bell (U.S. Pat. No. 2,394,423); H. Noyes et al. (U.S. Pat. No. 2,890,489); and R. E. Bailey (U.S. Pat. No. 2,558,807).
While the described prior art process and the techniques of the above-referenced prior art patents have been used successfully for many years, the primary disadvantage centers upon the use of the male form. Because the male form is destroyed in the process of removing it from the interior of the tank, a new form is required for each and every tank made. Thus, the costs attendent to the making of these type complex-shaped fuel tanks have risen dramatically because of the labor intensive nature of a process requiring hand-made male forms.
Furthermore, and because the composite forming the tank wall structure is laid up on the male form, it must be applied to a plurality of recesses which form the complex shape of the plaster mold. Irrespective of whether the composite is laid up by spraying or by hand application techniques, these recesses are critical areas of the tank structure and careful attention must be paid when applying the composite materials to these areas.
In view of the beforementioned disadvantages of the prior art tank manufacturing processes using male forms, it is according to one aspect of the present invention, an object to manufacture high technology, complex-shaped fuel tanks without resort to the use of male forms.
It is in accordance with another aspect of the invention, an object to provide a manufacturing process which results in a more accurate location of tank fittings and thus eliminates installation problems when the tank is mounted in a complex shaped vehicle cavity.
It is in accordance with still another aspect of the invention, an object to provide a fuel tank having more accurate exterior dimensions and the differences between subsequently manufactured tanks are kept to a minimum.